The use of image data, generally available in digital form, of a patient which were obtained prior to surgery, e.g. x-ray or computed tomography or magnetic resonance imaging recordings for planning and performing invasive surgical interventions, is known per se. Such methods provide “internal views” of organs or body parts. In some methods, these image data are also created or updated during the operation in order to visualize possible changes in the recorded object, e.g. the operation progress or reactions of the body to the surgical intervention, which are not detectable, or can only be detected badly, by film cameras or video cameras. Three-dimensional models of one or more body parts and/or organs can be calculated from image data obtained by tomography.
Moreover, it is conventional to record optical recordings such as photographs or video images of the patient intraoperatively, e.g. using an endoscope, and to display these on a monitor together with the tomographic image data created prior to surgery, respectively as an individual image or in a superposed manner. In this manner, it is possible, for example, to make tissue to be removed or nerve tracts or vessels, which are situated in the operation region and potentially endangered by the surgical intervention, more visible to the surgeon. This display of the image data allows the surgeon to use the medical devices used during the operation as efficiently as possible and with minimal adverse effects on the surrounding tissue of the patient.
Image data obtained by computed tomography (denoted tomographic image data below) or image data obtained by x-ray technology allow the visualization of regions in the human body which would require an invasive method for the creation of image data obtained by photography or video technology (denoted as F/V image data below). Instead, tomographic image data are disadvantageous in relation to F/V image data in that they generally do not depict the recorded regions true to scale but rather in a distorted manner. The distortion of the tomographic image data is due to the system and is not subject to predictable laws, according to which it could be corrected by predetermined correction algorithms. Inclusion of tomographic image data in a system for operation planning and/or intraoperative navigation, such as e.g. a position detection system, therefore requires rectification of the tomographic image data which is as error-free as possible in order to achieve the desired accuracy.
Known rectification methods compare the distorted tomographic image data with corresponding F/V image data which image the same region, preferably from the same perspective, and carry out rectification of the tomographic image data on the basis of the established deviations of the tomographic image data from the F/V image data. Subsequently, the image data for example can be depicted on a display in a superposed manner.
Such known methods for rectifying tomographic image data are disadvantageous in that they often produce erroneous results. A reason for this is that the same perspective cannot be obtained exactly when creating the tomographic image data and F/V image data, and hence rectification is carried out on the basis of F/V image data with a different perspective. Furthermore, the different image data are often created at different times, and so e.g. acute swelling, bruising, etc. can lead to errors when rectifying the tomographic image data.